The scope of this project is the study of infections of mink with the Aleutian disease of mink parvovirus (ADV). In the past year we developed strand-specific RNA hybridization probes to help localize sites of viral replication. The rationale for the probes is based on the fact that replicative forms of viral DNA (RFs) contain both "+" and "-" sense strands, but that the single stranded virion DNA (SS DNA) is greater than 90% "-" sense; thus, probes "+" in sense react with both the SS DNA and also with the duplex RFs, while "-" sense probes react preferentially with RFs. When tested against DNA extracted from mink infected with virulent ADV-Utah I strain, RFs were detected at 10 days after infection in mesenteric lymph node (MLN), liver, spleen, and gut, but only in gut and MLN at 43 days. SS DNA was noted in these tissues at 10, 43, and 60 days, and in contrast to infected permissive cell cultures, was more abundant than the RFs. These findings suggested that in adult mink, ADV may replicate in gut as well as lymphoreticular tissues. We also used these probes to investigate the recently described fulminant interstitial pneumonitis caused by ADV in newborn mink kits. This disease is characterized by gross pathological lesions confined to the lungs, the development of hyaline membranes, and the presence of viral inclusions. When histological lesions, the presence of intranuclear inclusion bodies, and intranuclear ADV antigen were correlated with levels of viral DNA species, it was concluded that the lung, probably alveolar type-II cells, is the major primary target for viral replication and cytopathology in kits. RFs were also found in low level in MLN, suggesting that ADV replicates in this organ, too, although no cytopathology was evident. The data suggested that the pattern of ADV replication in newborn lung tissue is similar to that seen in permissive cell cultures, but that the replication in other kit organs more closely resembles the pattern described for adult mink.